Project description:Silver nanoparticles (AgNPs), one of the most popular nanomaterials, are commonly used in consumer products and biomedical devices, despite their potential toxicity. Recently, AgNP exposure was reported to be associated with male reproductive toxicity in mammalian models. However, there is still a limited understanding of the effects of AgNPs on spermatogenesis. The fruit fly Drosophila testis is an excellent in vivo model to elucidate the mechanisms underlying AgNP-induced defects in spermatogenesis, as germ lineages can be easily identified and imaged. In this study, we evaluated AgNP-mediated toxicity on spermatogenesis by feeding Drosophila with AgNPs at various concentrations. We first observed a dose-dependent uptake of AgNPs in vivo. Concomitantly, AgNP exposure caused a significant decrease in the viability and delay in the development of Drosophila in a dose-dependent manner. Furthermore, AgNP-treated male flies showed a reduction in fecundity, and the resulting testes contained a decreased number of germline stem cells (GSCs) compared to controls. Interestingly, testes exposed to AgNPs exhibited a dramatic increase in reactive oxygen species levels and showed precocious GSC differentiation. Taken together, our study suggests that AgNP exposure may increase ROS levels in the Drosophila testis, leading to a reduction of GSC number by promoting premature GSC differentiation.
Project description:Emerging evidence supports that stem cells are regulated by both intrinsic and extrinsic mechanisms. However, factors that determine the fate of stem cells remain incompletely understood. The Drosophila testis provides an exclusive powerful model in searching for potential important regulatory factors and their underlying mechanisms for controlling the fate of germline stem cells (GSCs). In this study, we have found that Drosophila gilgamesh (gish), which encodes a homologue of human CK1-? (casein kinase 1-gamma), is required intrinsically for GSC maintenance. Our genetic analyses indicate gish is not required for Dpp/Gbb signaling silencing of bam and is dispensable for Dpp/Gbb signaling-dependent Dad expression. Finally, we show that overexpression of gish fail to dramatically increase the number of GSCs. These findings demonstrate that gish controls the fate of GSCs in Drosophila testis by a novel Dpp/Gbb signaling-independent pathway.
Project description:Reactive oxygen species (ROS) are byproducts generated during normal cellular metabolism, and redox states have been shown to influence stem cell self-renewal and lineage commitment across phyla. However, the downstream effectors of ROS signaling that control stem cell behavior remain largely unexplored. Here, we used the Drosophila testis as an in vivo model to identify ROS-induced effectors that are involved in the differentiation process of germline stem cells (GSCs). In the Affymetrix microarray analysis, 152 genes were either upregulated or downregulated during GSC differentiation induced by elevated levels of ROS, and a follow-up validation of the gene expression by qRT-PCR showed a Spearman's rho of 0.9173 (P<0.0001). Notably, 47 (31%) of the identified genes had no predicted molecular function or recognizable protein domain. These suggest the robustness of this microarray analysis, which identified many uncharacterized genes, possibly with an essential role in ROS-induced GSC differentiation. We also showed that maf-S is transcriptionally downregulated by oxidative stress, and that maf-S knockdown promotes GSC differentiation but Maf-S overexpression conversely results in an over-growth of GSC-like cells by promoting the mitotic activity of germ cell lineage. Together with the facts that Maf-S regulates ROS levels and genetically interacts with Keap1/Nrf2 in GSC maintenance, our study suggests that Maf-S plays an important role in the Drosophila testis GSC maintenance by participating in the regulation of redox homeostasis.
Project description:Gap junction (GJ) proteins, the primary constituents of GJ channels, are conserved determinants of patterning. Canonically, a GJ channel, made up of two hemi-channels contributed by the neighboring cells, facilitates transport of metabolites/ions. Here we demonstrate the involvement of GJ proteins during cuboidal to squamous epithelial transition displayed by the anterior follicle cells (AFCs) from Drosophila ovaries. Somatically derived AFCs stretch and flatten when the adjacent germline cells start increasing in size. GJ proteins, Innexin2 (Inx2) and Innexin4 (Inx4), functioning in the AFCs and germline respectively, promote the shape transformation by modulating calcium levels in the AFCs. Our observations suggest that alterations in calcium flux potentiate STAT activity to influence actomyosin-based cytoskeleton, possibly resulting in disassembly of adherens junctions. Our data have uncovered sequential molecular events underlying the cuboidal to squamous shape transition and offer unique insight into how GJ proteins expressed in the neighboring cells contribute to morphogenetic processes.
Project description:Germ cells develop in a microenvironment created by the somatic cells of the gonad [1-3]. Although in males, the germ and somatic support cells lie in direct contact, in females, a thick extracellular coat surrounds the oocyte, physically separating it from the somatic follicle cells [4]. To bypass this barrier to communication, narrow cytoplasmic extensions of the follicle cells traverse the extracellular coat to reach the oocyte plasma membrane [5-9]. These delicate structures provide the sole platform for the contact-mediated communication between the oocyte and its follicular environment that is indispensable for production of a fertilizable egg [8, 10-15]. Identifying the mechanisms underlying their formation should uncover conserved regulators of fertility. We show here in mice that these structures, termed transzonal projections (TZPs), are specialized filopodia whose number amplifies enormously as oocytes grow, enabling increased germ-soma communication. By creating chimeric complexes of genetically tagged oocytes and follicle cells, we demonstrate that follicle cells elaborate new TZPs that push through the extracellular coat to reach the oocyte surface. We further show that growth-differentiation factor 9, produced by the oocyte, drives the formation of new TZPs, uncovering a key yet unanticipated role for the germ cell in building these essential bridges of communication. Moreover, TZP number and germline-soma communication are strikingly reduced in reproductively aged females. Thus, the growing oocyte locally remodels follicular architecture to ensure that its developmental needs are met, and an inability of somatic follicle cells to respond appropriately to oocyte-derived cues may contribute to human infertility.
Project description:BackgroundSexual dimorphism results in the formation of two types of individuals with specialized reproductive roles and is most evident in the germ cells and gonads.ResultsWe have undertaken a global analysis of transcription between the sexes using a 31,464 element FlyGEM microarray to determine what fraction of the genome shows sex-biased expression, what tissues express these genes, the predicted functions of these genes, and where these genes map onto the genome. Females and males (both with and without gonads), dissected testis and ovary, females and males with genetically ablated germlines, and sex-transformed flies were sampled.ConclusionsUsing any of a number of criteria, we find extensive sex-biased expression in adults. The majority of cases of sex differential gene expression are attributable to the germ cells. There is also a large class of genes with soma-biased expression. There is little germline-biased expression indicating that nearly all genes with germline expression also show sex-bias. Monte Carlo simulations show that some genes with sex-biased expression are non-randomly distributed in the genome.
Project description:Hormesis is a biological phenomenon, whereby exposure to low levels of toxic agents or conditions increases organismal viability. It thus represents a beneficial aspect of adaptive responses to harmful environmental stimuli. Here we show that hormesis effects induced in the parental generation can be passed on to the descendants in Caenorhabditis elegans. Animals subjected to various stressors during developmental stages exhibit increased resistance to oxidative stress and proteotoxicity. The increased resistance is transmitted to the subsequent generations grown under unstressed conditions through epigenetic alterations. Our analysis reveal that the insulin/insulin-like growth factor (IGF) signalling effector DAF-16/FOXO and the heat-shock factor HSF-1 in the parental somatic cells mediate the formation of epigenetic memory, which is maintained through the histone H3 lysine 4 trimethylase complex in the germline across generations. The elicitation of memory requires the transcription factor SKN-1/Nrf in somatic tissues. We propose that germ-to-soma communication across generations is an essential framework for the transgenerational inheritance of acquired traits, which provides the offspring with survival advantages to deal with environmental perturbation.
Project description:During the evolution of heteromorphic sex chromosomes, the sex-specific Y chromosome degenerates, while the X chromosome evolves new mechanisms of regulation. Using bioinformatic and experimental approaches, we investigate the expression of the X chromosome in Drosophila melanogaster. We observe nearly complete X chromosome dosage compensation in male somatic tissues, but not in testis. The X chromosome contains disproportionately fewer genes with high expression in testis than the autosomes, even after accounting for the lack of dosage compensation, which suggests that another mechanism suppresses their expression in the male germline. This is consistent with studies of reporter genes and transposed genes, which find that the same gene has higher expression when autosomal than when X-linked. Using a new reporter gene that is expressed in both testis and somatic tissues, we find that the suppression of X-linked gene expression is limited to genes with high expression in testis and that the extent of the suppression is positively correlated with expression level.